Analysis of the composition of a sample is necessary in the manufacture of many different types of devices. The composition of a sample is the concentration of an element and/or chemical species in a thin film. An example of a sample that may require composition analysis is a gate oxide film formed in a semiconductor integrated circuit device. As the density of an integrated circuit chip in a semiconductor device increases and the dimensions of the device continue to be reduced, sample analysis becomes harder and more complex.
For example, recent developments in the fabrication of semiconductor devices may employ shallow implant and/or other ultra-thin structures.
In one particular example, gate oxide layers are becoming very thin films, typically less than about 10 nanometers in thickness. Such thin films are difficult to characterize. Such structures will require characterization techniques that have improved sensitivity over conventional characterization techniques. Further, such techniques may also require the characterization to be performed with ample speed.
Various techniques have been used for surface analysis of trace and/or major components in such materials. For example, several of such methods include secondary ion mass spectrometry (SIMS), x-ray photoelectron spectrometry (XPS) (also known as electron spectroscopy for chemical analysis (ESCA)), and Auger electron spectrometry (AES). Such techniques are sensitive to the near-surface region of a material. However, these techniques do not permit measurement of material properties as a function of depth beneath the surface through depth profiling.
In a typical depth profiling process, for example, continuous or periodic ion beam sputtering removes material from the surface of a sample to expose progressively deeper material at one or more various depths of the sample for further measurement and/or analysis. Generally known sputter rates may be used to determine the depth at which the surface measurements are completed. As such, a characterization of the sample as a function of depth beneath the surface can be attained using SIMS, XPS, or AES.
Many of the techniques described above for characterizing thin films are invasive techniques, e.g., they involve destruction of at least one or more portions of the sample. Such techniques, e.g., those that use removal of material during depth profiling, are sufficient in many circumstances, e.g., research and development, product testing, etc., but do not provide for the ability to quickly analyze a thin film such as is necessary in production processes. For example, in such production processes, a thin film being formed typically needs to be analyzed so that such information can be used for production control, product test, etc., without loss of product due to invasive characterization of such films.